Parking brake system

Abstract

In a parking brake system, a locking tooth of a ratchet plate includes a first area for contacting and retaining a locking claw of a ratchet pawl in an equilibrium state when a parking brake lever is pulled up; and a second area in which the locking claw remains in a state of halfway engagement of tooth tips when a pressing force of a release rod is released. When the locking claw comes into contact with a portion closer to a tip of the locking tooth beyond the first area, a line of force is maintained due to the pressing force of the release rod. The system is configured such that even if an occupant erroneously pulls up the parking brake lever while the release rod is pressed, it is possible to reliably prevent halfway engagement of tooth tips in a ratchet mechanism.

The invention claimed is: 
     
       1. A parking brake system comprising:
 a parking brake lever which is capable of being pulled up so as to drag a brake cable, and is swingably pivotally supported on a bracket which is connected to a vehicle body, the parking brake lever comprising a base portion which is pivotally supported on the bracket by a pivot connection, and a grip portion extending upwardly from the base portion; 
 a ratchet pawl pivotally supported on the parking brake lever via a fulcrum pin, the ratchet pawl having a spring engagement portion at a first end thereof, and a locking claw at a second end thereof, wherein a predetermined clearance is provided between the ratchet pawl and the fulcrum pin; 
 a ratchet plate affixed to the bracket, and including a plurality of locking teeth and a plurality of locking grooves arranged alternately, wherein the locking claw of the ratchet pawl is capable of engaging with the locking teeth and the locking grooves; 
 a release rod configured to press the ratchet pawl in accordance with an occupant's release operation to make the ratchet pawl swing in a direction in which the locking claw is disengaged from the locking grooves; and 
 a torsion spring mounted on a boss on the base portion of the parking brake lever, the torsion spring having a first end operatively connected to a lower end portion of the release rod, and a second end operatively connected to the spring engagement portion of the ratchet pawl; 
 wherein a direction of a first straight line and a direction of a second straight line are set different from each other, the first straight line representing a straight line on which a point of contact between the ratchet pawl and the release rod, a center of an arc of one of the locking teeth and a center of an arc of the locking claw exist while a tip of the locking tooth and a tip of the locking claw are in contact with each other, the second straight line representing a straight line on which a point of contact between the fulcrum pin and the ratchet pawl, the center of the arc of the locking tooth, and the center of the arc of the locking claw exist while the tip of the locking tooth and the tip of the locking claw are in contact with each other, 
 wherein when the release rod is disengaged, the locking claw moves from a position where the first straight line is established, toward a position where the locking claw is engaged with the locking groove while the ratchet pawl moves by said predetermined clearance, 
 and wherein each of the locking teeth includes a respective tip end portion having an arcuate outline shape defining a respective tooth tip radial center point, and the ratchet claw includes a tip end portion formed in an arcuate outline shape defining a claw tip radial center point, to promote sliding movement of the ratchet claw in relation to a tooth tip during operation of the parking brake system. 
 
     
     
       2. The parking brake system according to  claim 1 , wherein:
 a first equilibrium state takes place in a case where, when an occupant's pulling-up force on the parking brake lever is substantially equal to a tensile force of the brake cable, the tip of a locking tooth and the tip of the locking claw come into contact with each other due to a pressing force of the release rod on the ratchet pawl, and the first straight line exists under this condition, 
 a second equilibrium state takes place in a case where, when the occupant's pulling-up force on the parking brake lever is substantially zero, the tip of the locking tooth and the tip of the locking claw come into contact with each other due to the tensile force of the brake cable, and the second straight line exists under this condition, and 
 the first equilibrium state and the second equilibrium state take place, respectively, in predetermined areas, each of whose centers is a point of contact between the locking tooth and the locking claw. 
 
     
     
       3. The parking brake system of  claim 1 , wherein when the release rod is disengaged, the ratchet pawl moves while the fulcrum pin moves by said clearance, whereby the ratchet pawl is displaced from a tooth tip side of the locking tooth in an engagement direction. 
     
     
       4. The parking brake system of  claim 1 , wherein the ratchet pawl is pivotally supported on the parking brake lever via a single fulcrum pin, and the ratchet pawl comprises a central portion having a single hole formed therein to receive the fulcrum pin, said hole being larger than the fulcrum pin to provide said predetermined clearance. 
     
     
       5. The parking brake system of  claim 4 , wherein:
 a boss portion is provided on a base portion of the parking brake lever, 
 a torsion spring is mounted on said boss portion, and 
 the release rod is connected to the ratchet pawl only by said torsion spring. 
 
     
     
       6. The parking brake system of  claim 1 , wherein said locking teeth have a first area in which a first equilibrium state occurs between the locking teeth and the locking claw when the release rod presses the ratchet pawl, and a second area in which a second equilibrium state occurs between the locking teeth and the locking claw when the ratchet pawl receives a load from the fulcrum pin, wherein said first area and said second area are not overlapped with each other. 
     
     
       7. The parking brake system of  claim 1 , wherein the release rod is connected to the ratchet pawl only by said torsion spring.